This invention relates to novel processes for direct production of foamed articles from a polymer latex without a need for any chemical or mechanical blowing agent, as well as to processes for the adherent coating of a substrate with a water-borne polymer. In the foam process, articles are produced by freezing of the latex in a mold, followed by removal of the water, to give a foam having an open cell structure with foam density inversely affected by the level of solids in the latex. “Mold” is used in a broad sense to cover three dimensional molds as well as objects onto which the dispersion to be foamed is applied, such as by spraying or dipping. The foams are used in a variety of applications such as comfort cushioning in automobiles and airplanes; for thermal and acoustic insulation; for shock absorption; and the like. The coatings are applied to a wide variety of substrates such as metal, glass, stone, brick, tile, cementitious materials, mortar, natural and synthetic fibers, cloth, paper, leather, and woven and nonwoven fabrics.
An example of polymers for these applications are fluoropolymers, more specifically copolymers of vinylidene fluoride (VDF) and hexafluoropropylene (HFP) and still more specifically copolymers having very low or no crystallinity. For coatings, the copolymers at all levels of HFP content remain highly flexible, thermoplastic copolymers which show low surface tack even at high HFP levels and thereby permit use of such copolymers in unique applications for which polyvinylidene fluoride homo- and copolymers previously known were not considered suitable, or were considered suitable only when combined with other polymers or other materials such as primers and the like.
Low crystallinity fluorinated polymers are highly useful, particularly as coating and encapsulants, because of their low surface energy, low refractive index, good chemical resistance, and the relative ease of coating or encapsulating objects with such inert polymers. The balance between amorphous and crystalline regions, the nature and extent of the crystalline regions, and the interphase between these regions affects the processability options to obtain articles having the beneficial attributes and hence, the ultimate applications for a given resin composition. Low crystallinity fluorinated polymers are defined in WO 01/32726, the disclosure of which is incorporated herein by reference.
Copolymers of VDF and HFP vary in their properties. At one end of the spectrum there are totally amorphous thermoplastic polymers and at the other extreme the highly crystalline polymers. The microstructure of the polymer chain determines the flexibility (or alternately the stiffness) at a given temperature. This mechanical behavior is controlled by the type and amount of the crystalline phase (if any) and the dynamics of the molecular motion along the chain such that at some temperature the polymer undergoes a second order change in response to applied stresses, the so-called glass transition temperature (Tg). Above the Tg the polymer chain has molecular motions which are free to rotate, stretch, etc. and thereby absorb the energy input. Below the Tg the molecular motions are frozen and the stresses may lead to brittle fracture or glass-like behavior.
Applicant is not aware of prior art disclosing the foam process. However, certain prior art is noted below relating to coating applications.